Method of supporting data retransmission in a mobile communication system

ABSTRACT

A method of supporting packet transmission in a mobile communication system is disclosed according to the present invention. A method of transmitting packets at a user equipment in a mobile communication system comprises transmitting a first packet to a network and transmitting a second packet to the network regardless of a reception status signal for the first packet, when control information for the second packet is received from the network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/303,246, filed on Dec. 2, 2008, now U.S. Pat. No. 8,234,534, which isthe National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2007/002785, filed on Jun. 8, 2007, which claimsthe benefit of earlier filing date and right of priority to KoreanApplication No. 10-2007-0003092, filed on Jan. 10, 2007, and also claimsthe benefit of U.S. Provisional Application Ser. Nos. 60/863,545, filedon Oct. 30, 2006, and 60/815,722, filed on Jun. 21, 2006, the contentsof which are all incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a mobile communication system, moreparticularly, to a method of supporting data retransmission in a Mobilecommunication system.

BACKGROUND ART

Recently, an auto repeat request (ARQ) or hybrid auto repeat request(HARQ) scheme is widely used in order to performing effectivecommunications by increasing throughput in a mobile communicationsystem.

The ARQ or HARQ is a scheme whereby a receiving side transmitsinformation on whether received data has a reception error to atransmitting side, so that the transmitting side can retransmit datahaving the reception error. In other words, in a system supporting theARQ or HARQ scheme, the receiving side transmits, to the transmittingside, positive reception acknowledgement (ACK) for a packet successfullyreceived from the transmitting side, whereas the receiving sidetransmits, to the transmitting side, negative reception acknowledgement(NACK) for a data packet unsuccessfully received so that thetransmitting side retransmits the data packet for which NACK isreceived.

FIG. 1 is a diagram illustrating an HARQ scheme in a WCDMA system inaccordance with a conventional art. Referring to FIG. 1, a base stationdetermines a user equipment (UE) to which a packet is to be transmittedand a format (a coding rate, a modulation scheme, and data amount, etc)of the packet. The base station transmits control information for thepacket to the user equipment on a downlink control channel (HS-SCCH) andthen transmits the packet to the user equipment on a downlink datachannel (HS-DSCH) at a certain time associated with the transmittingtime of the control information.

After receiving the packet from the base station, the user equipmentdecodes the received packet. If the packet is successfully decoded, theuser equipment transmits ACK to the base station through an uplinkchannel. The base station receiving ACK from the user equipment-realizesthat the packet has been successfully transmitted to the user equipmentand transmits a next packet. If the user equipment fails to successfullydecode the received packet, the user equipment transmits NACK to thebase station. The base station receiving NACK from the user equipmentconfigures a retransmission packet which has an identical or new packetformat and transmits the retransmission packet to the user equipment.The user equipment tries to decode the retransmission data by combiningthe retransmission packet with the initial packet in various ways.

In adopting the ARQ or HARQ scheme, it is necessary for a transmittingside to receive ACK or NACK from a receiving side with significantreliability. In case that the transmitting side receives and decodes ACKor NACK erroneously, radio resources can be wasted by transmitting aretransmission packet which is unnecessary since the receiving sidereceives an initial packet successfully or by transmitting a new packetalthough retransmission of an initial packet is necessary since thereceiving side fails to successfully receive the initial packet. Forexample, when a user equipment obtains NACK by erroneously receiving ordecoding ACK received from a base station, the user equipmentretransmits an initial packet to the base station. In this case, thebase station considering that the initial packet has been successfullyreceived may allocates, to another user equipment, radio resources whichshould be allocated to the user equipment. In this case, the first userequipment retransmits the initial packet and the second user equipmenttransmits a new packet through the identical radio resources. As aresult, the base station cannot receive the retransmission packet fromthe first user equipment nor the new packet from the second userequipment successfully because of a data collision between theretransmission packet and the new packet on the identical radioresources.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method of supportingdata retransmission in a mobile communication system that substantiallyobviates one or more of the problems due to limitations anddisadvantages of the related art.

One object of the present invention is to provide a method of supportinga retransmission scheme in a mobile communication system, wherebytransmission reliability of positive reception acknowledgement (ACK) ornegative reception acknowledgement (NACK) can be increased.

Another object of the present invention is to provide a method ofsupporting a retransmission scheme in a mobile communication system,whereby communication efficiency can be increased.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention is embodied in a method of supporting a hybrid automaticrepeat and request (HARQ) in a mobile communication system, the methodcomprising receiving a packet from a user equipment, decoding thereceived packet, transmitting a reception status signal for the packetaccording to the decoding result, and transmitting supplemental controlinformation indicating that the reception status signal is a positiveacknowledgement signal (ACK) when the received packet is successfullydecoded.

In one aspect of the present invention, a method of supporting a hybridautomatic repeat and request (HARQ) at a user equipment in a mobilecommunication system comprises transmitting a first packet to a network,receiving a reception status signal for the first packet from thenetwork, obtaining a negative acknowledgement signal (NACK) by decodingthe reception status signal, and receiving supplemental controlinformation indicating that the reception status signal is a positiveacknowledgement signal (ACK).

In another aspect of the present invention, a method of supporting ahybrid automatic repeat and request (HARQ) at a user equipment in amobile communication system comprises transmitting a first packet to anetwork, receiving a reception status signal for the first packet fromthe network, receiving an uplink scheduling grant message allocatinguplink resources for transmitting a second packet from the network, andperforming a next procedure on an assumption that the first packet issuccessfully received by the network.

In still another aspect of the present invention, a user equipment forsupporting a hybrid automatic repeat and request (HARQ) in a mobilecommunication system is adapted to perform the steps of transmitting afirst packet to a network, receiving a reception status signal for thefirst packet from the network, obtaining a negative acknowledgementsignal (NACK) by decoding the reception status signal, and receivingsupplemental control information indicating that the reception statussignal is a positive acknowledgement signal (ACK).

In further still another aspect of the present invention, a userequipment for supporting a hybrid automatic repeat and request (HARQ) amobile communication system is adapted to perform the steps oftransmitting a first packet to a network, receiving a reception statussignal for the first packet from the network, receiving an uplinkscheduling grant message allocating uplink resources for transmitting asecond packet from the network, and performing a next procedure on anassumption that the first packet is successfully received by thenetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a diagram illustrating an HARQ scheme in a WCDMA system inaccordance with a conventional art.

FIG. 2 is a block diagram of a network structure of E-UMTS (evolveduniversal mobile telecommunications system);

FIG. 3 is a schematic diagram illustrating a protocol architecture of anE-UTRAN.

FIG. 4A and 4B are architectural diagrams of a control plane and a userplane, respectively of a radio interface protocol between UE (userequipment) and UTRAN (UMTS terrestrial radio access network) based onthe 3GPP radio access network standard;

FIG. 5 is a diagram illustrating a structure of physical channels in theE-UMTS;

FIG. 6 is a flow diagram illustrating an embodiment of the presentinvention; and

FIG. 7 is a flow diagram illustrating a procedure in a user equipment inaccordance with an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 is a block diagram of a network structure of an E-UMTS(Evolved-Universal Mobile Telecommunications System) to which technicalfeatures of the present invention are applied. An E-UMTS is a systemevolving from the conventional UMTS and its basic standardization iscurrently handled by the 3GPP (3^(rd) Generation Partnership Project).The E-UMTS can also be called an LTE (Long Term Evolution) system.Release 7 and Release 8 of 3GPP technical specifications (3^(rd)Generation Partnership Project; Technical Specification Group RadioAccess Network) can be referred to obtain detailed information about theUMTS and E-UMTS,

Referring to FIG. 2, an E-UMTS network includes a user equipment(hereinafter abbreviated ‘UE’), a base station (hereinafter named ‘eNodeB’ or ‘eNB’) and an access gateway (hereinafter abbreviated ‘aGW’)connected to an external network by being located at an end of theE-UMTS network. The aGW may be classified into a part for handling usertraffic and a part for handling control traffic. A first aGW forprocessing new user traffic may communicate with a second AG forprocessing control traffic via a new interface. A eNode-B may include atleast one cell. A first interface for transmitting user traffic or asecond interface for transmitting control traffic may be located betweenseveral eNode-Bs. The CN may include the aGW and a plurality of nodesfor registering users of User Equipments (UEs). If required, anotherinterface for discriminating between the E-UTRAN and the ON may also beused for the LTE network. The aGW manages mobility of a UE by unit of atracking area (TA). A TA comprises a plurality of cells. When a UE movesinto a TA from another TA, the UE informs the aGW of the change of theTAs. The eNode B includes at least one cell.

FIG. 3 is a schematic diagram illustrating protocol architecture of anE-UTRAN. In FIG. 2, the hatching part represents functional entities ofa control plane and the non-hatching part represents functional entitiesof a user plane.

Layers of a radio interface protocol between a UE and a network can beclassified into a first layer L1, a second layer L2 and a third layer L3based on three lower layers of OSI (open system interconnection)reference model widely known in communication systems. A physical layerbelonging to the first layer L1 provides an information transfer serviceusing a physical channel. A radio resource control (hereinafterabbreviated ‘RRC’) located at the third layer plays a role incontrolling radio resources between the UE and the network. For this,the RRC layer enables RRC messages to be exchanged between the UE andthe network. The RRC layer can be distributively located at networknodes including an eNode B, an AG and the like or at either the Node Bor the AG.

FIGS. 4A and 4B are architectural diagrams of a control plane and a userplane, respectively of a radio interface protocol between UE (userequipment) and UTRAN (UMTS terrestrial radio access network) based onthe 3GPP radio access network standard. Referring to FIG. 4A, a radiointerface protocol vertically includes a physical layer, a data linklayer, and a network layer and horizontally includes a user plane fordata information transfer and a control plane for signaling transfer.The protocol layers in FIG. 4A can be classified into L1 (first layer),L2 (second layer), and L3 (third layer) based on three lower layers ofthe open system interconnection (OSI) standard model widely known in thecommunications systems.

The respective layers of a radio protocol control plane shown in FIG. 4Aand a radio protocol user plane shown in FIG. 4B are explained asfollows.

First of all, the physical layer as the first layer provides informationtransfer service to an upper layer using physical channels. The physicallayer (PHY) is connected to a medium access control (hereinafterabbreviated ‘MAC’) layer above the physical layer via transportchannels. Data are transferred between the medium access control layerand the physical layer via the transport channels. Moreover, data istransferred between different physical layers, and more particularly,between one physical layer of a transmitting side and the other physicallayer of a receiving side via the physical channels. A downlink physicalchannel of the E-UMTS is modulated according to an orthogonal frequencydivision multiplexing (OFDM) scheme and time and frequency are used asradio resources.

The medium access control (hereinafter abbreviated ‘MAC’) layer of thesecond layer provides a service to a radio link control (hereinafterabbreviated RLC) layer above the MAC layer via logical channels. The RLClayer of the second layer supports reliable data transfer. In order toeffectively transmit IP packets (e.g., IPv4 or IPv6) within aradio-communication period having a narrow bandwidth, a PDCP layer ofthe second layer (L2) performs header compression to reduce the size ofa relatively-large IP packet header containing unnecessary controlinformation.

A radio resource control (hereinafter abbreviated ‘RRC’) layer locatedon a lowest part of the third layer is defined in the control plane onlyand is associated with configuration, reconfiguration and release ofradio hearers (hereinafter abbreviated ‘RBs’) to be in charge ofcontrolling the logical, transport and physical channels. In this case,the RB means a service provided by the second layer for the datatransfer between the UE and the UTRAN.

As a downlink transport channel carrying data to UEs from the network,there is a broadcast channel (BCH) carrying system information and adownlink shared channel (SCH) carrying user traffic or control messages.The traffic or control messages of a downlink multicast or broadcastservice can be transmitted via the downlink SCH or an additionaldownlink multicast channel (MCH). Meanwhile, as an uplink transportchannel carrying data to the network from UEs, there is a random accesschannel (RACH) carrying an initial control message and a uplink sharedchannel (UL-SCH) carrying user traffic or control message.

In the E-UMTS system, an OFDM is used on the downlink and a singlecarrier frequency division multiple access (SC-FDMA) on the uplink. TheOFDM scheme using multiple carriers allocates resources by unit ofmultiple sub-carriers including a group of carriers and utilizes anorthogonal frequency division multiple access (OFDMA) as an accessscheme.

A physical layer of an OFDM or OFDMA scheme divides active carriers intoa plurality of groups and transmits each group to a different receivingside. Radio resource allocated to each UE which is defined as atime-frequency region on a two-dimensional sphere comprises continuoussub-carriers on a frequency axis and symbols on a time axis. Atime-frequency region in the OFDM or OFDMA scheme is a rectangular formsectioned by time and frequency coordinates. One or more time-frequencyregion can be allocated to an uplink for a UE and an eNB can transmitone or more time-frequency region to a UE. In order to define atime-frequency region on the two-dimensional sphere, the number of OFDMsymbols and sub-carriers starting from a point having an offset from areference point should be given.

The E-UMTS uses 10 ms radio frame comprising 20 sub-frames. Namely, asub-frame is 0.5 ms length. A resource block comprises one sub-frame andtwelve sub-carriers, each of which is 15 kHz. One sub-frame comprises aplurality of OFDM symbols and a part of the plurality of OFDM symbolscan be used for L1/2 control information.

FIG. 5 is a diagram illustrating a structure of physical channels in theE-UMTS. In FIG. 5, a sub-frame comprises a L1/2 control informationtransmission region (the hatching part) and a data transmission region(the non-hatching part).

One embodiment of an HARQ scheme applicable to the E-UMTS system will bedescribed as follows.

A base station which transmits downlink data to user equipments based onthe HARQ scheme transmits downlink (DL) scheduling information on a DLL1/2 control channel to a user equipment (UE).

The DL scheduling information may include an identifier (ID) for a UE ora UE group, information about downlink radio resources allocated for DLdata transmission (region, duration, etc), a modulation scheme, a sizeof payload, transmission parameters like information on multi-inputmulti-output (MIMO), etc, HARQ process information, a redundancy versionand a new data indicator indicating whether data is new or not, etc.

Basically, the DL scheduling information can be transmitted on the DLL1/2 control information during data retransmission. The contents of theDL scheduling information can vary according to channel environments.For example, in case that the channel environment is better than that ofan initial transmission, data having higher data rate can be transmittedby changing a modulation scheme or a size of payload. On the other hand,in case that the channel environment is worse than the initialtransmission, data of lower data rate can be transmitted.

The user equipment obtains the DL scheduling information by monitoringthe DL L1.2 control channel in every transmit time interval (TTI) andthen receives data from the base station by using the DL schedulinginformation.

However, because the amount of information which can be transmittedthrough the DL L1/2 control channel is limited, it is difficult for theDL scheduling information for plurality of user equipments to betransmitted in a single TTI. In this reason, the DL schedulinginformation can be transmitted during an initial data transmission onlyand can be used for data retransmissions thereafter without transmittingfurther DL scheduling information. A user equipment monitoring the DLL1/2 control information receives a packet in accordance with DLscheduling information, if the DL scheduling information includes anidentifier of the user equipment.

In case that the user equipment fails to successfully receive thepacket, the user equipment requests data retransmission by transmittingNACK to the base station. The base station transmits a retransmissionpacket to the user equipment without transmitting DL schedulinginformation. In other words, the user equipment which has transmittedNACK to the base station can receive the retransmission packet in apredetermined time period based on the DL scheduling informationreceived during the initial transmission. With the above dataretransmission scheme, radio resources can be saved since DL schedulinginformation for retransmission data does not need to be transmitted.

FIG. 6 is a flow diagram illustrating an embodiment of the presentinvention. The embodiment of FIG. 6 is an example for obviating asituation that a user equipment erroneously retransmits a packet bymisunderstanding ACK from a network (UTRAN or E-UTRAN) as NACK owing todeterioration of channel environments, etc.

Referring to FIG. 6, a user equipment transmits a data packet to anetwork [S61]. Receiving and decoding the packet [S62], the networktransmits ACK or NACK to the user equipment according to the decodingresult [S63]. Namely, the network transmits ACK to the user equipment incase that the packet is successfully decoded, otherwise NACK istransmitted.

When the network transmits ACK to the user equipment, the networktransmits an uplink scheduling grant message through a DL L1/2 controlchannel [S64]. The uplink scheduling grant message can includes twokinds of information. First, in case that it is necessary for thenetwork to allocate radio resources to the user equipment, the uplinkscheduling grant message includes radio resource allocation information.Second, in case that it is unnecessary for the network to allocate radioresources to the user equipment, the uplink scheduling grant messageincludes supplemental control information. The supplemental controlinformation is information indicating that the network has transmittedACK for the packet received from the user equipment, whereby obviating asituation that the user equipment misunderstands ACK transmitted by thenetwork as NACK.

The necessity of allocating the radio resources to the user equipmentcan be determined based on whether the user equipment stores data to betransmitted in its buffer, namely based on status of the buffer of theuser equipment. In other words, when the user equipment has data to betransmitted to the network, it is necessary for the network to allocatethe radio resources for transmitting the data, otherwise allocation ofthe radio resources is unnecessary.

The network is able to obtain the buffer status of the user equipmentthrough a buffer status report received from the user equipmentperiodically or if a specific event occurs. The user equipment caninform the network when the last packet is transmitted through a MACprotocol data unit (PDU). For example, in case that two MAC PDUs arestored in the buffer of the user equipment, the user equipment transmitsa first MAC PDU including information indicating that one MAC PDU isstored in the buffer, whereby informing the network that there remainsone MAC PDU in the buffer. More specifically, when the N^(th) MAC PDU isthe last data stored in the buffer of the user equipment, the userequipment makes control information indicating that the N^(th) MAC PDUis the last data included in the (N−1)^(th) MAC PDU including, whentransmitting the (N−1)^(th) MAC PDU. As a specific example, eitherexisting or newly added one bit of MAC PDU can be used as the controlinformation. When the one bit can be used in a way that the one bit of‘0’ indicates that there are two or more MAC PDUs in the buffer and theone bit of ‘1’ indicates that there is one MAC PDU in the buffer.

The supplemental control information can be included in the uplinkscheduling grant message in various formats within a scope of indicatingthe actual meaning. For example, the following embodiments can beconsidered.

First, the supplemental control information can be included in a waythat at least one field of the uplink scheduling grant message is set tohave a predefined value. For example, every bit of the at least onefield can be set to have a value of ‘0’. More specifically, as describedabove, the uplink scheduling grant message includes a plurality offields to include a UE identifier, a UE group identifier, location andduration of allocated radio resources, and transmission parameters. Asthe supplemental control information, all bits of all or a part of thefields other than a field for the UE or UE group identifier can be setto have a value of ‘0’. Alternatively, one bit or two or moreconsecutive bits of a field can be set to have a meaning of thesupplemental control information. For example, the field for theduration of allocated radio resources can be set to have values of‘111’.

Second, a field including the supplemental control information can beadded to the uplink scheduling grant message. For example, one bit canbe newly added to the uplink scheduling grant message. The uplinkscheduling grant message can be used in a way that if the added bit isset to have a value of ‘0’, the uplink scheduling grant message isinterpreted to be used for radio resource allocation and if the addedbit is set to have a value of ‘1’, the uplink scheduling grant messageis interpreted to be used for transferring the supplemental controlinformation.

As another embodiment, the supplemental control information can beincluded in an independent control message to be transmitted to the userequipment other than the uplink scheduling grant message. The controlmessage including the supplemental message can be transmitted on theL1/2 control channel or a downlink shared channel (DL-SCH). For example,the supplemental control information can be transmitted to the userequipment by using a control message having a size of one or more bitson the DL L1/2 control channel. In this case, radio resources fortransmitting the control message can be allocated to each user equipmentin advance. Namely, when a radio bearer (RB) is established, the radioresources for the control message can be allocated through a radioresource control (RRC) message.

As a specific example, in case that it is unnecessary for the network toallocate radio resource to the user equipment when the network transmitsACK to the user equipment, a hit of the control message is set to have avalue of ‘1’ to be transmitted to the user equipment.

The user equipment may or may not transmit a new data packet inaccordance with ACK/NACK and the supplemental control information [S65].

FIG. 7 is a flow diagram illustrating a procedure in a user equipment inaccordance with an embodiment of the present invention. The userequipment operates differently depending on whether the user equipmentreceives ACK or NACK from the network and whether the user equipmentreceives the supplemental control information or not.

Referring to FIG. 7, the user equipment transmits a data packet to thenetwork [S71]. The user equipment receives ACK or NACK from the network[S72]. When receiving ACK, the user equipment transmits a new packet tothe network through radio resources allocated from the network. In casethat the user equipment receives ACK and the supplemental controlinformation from the network, the user equipment realizes that thenetwork receives the packet successfully.

When the user equipment receives NACK from the network, the userequipment examines whether new radio resources are allocated to the userequipment [S73]. In case that the new radio resources are allocated tothe user equipment, the user equipment determines whether the packet issuccessfully received by the network in the following ways.

In case that the number of packet transmissions is greater than apredetermined maximum number of retransmission, the user equipmentinterprets that the network has failed to successfully receive thepacket and informs an upper layer of the fact, so that enables the upperlayer to retransmit the packet according to protocols of the upperlayer. In case that the number of packet transmissions is not greaterthan the predetermined maximum number of retransmission, the userequipment transmits a new packet through the allocated radio resources.In other words, when the new radio resources are allocated to the userequipment though the user equipment has received NACK from the network,the user equipment realizes that NACK has been erroneously received bythe network though the network has transmitted ACK to the userequipment. Accordingly, the user equipment considers that the packet hasbeen received successfully by the network and does not transmit aretransmission packet.

In case that new radio resources are not allocated to the userequipment, the user equipment examines whether the supplemental controlinformation is received from the network [S74]. When the supplementalcontrol information is received, the user equipment regards the receivedNACK as ACK and considers that the network has successfully received thepacket. A lower layer of the user equipment informs an upper layer thatthe network has successfully received the packet. The upper layer doesnot consider retransmission of the packet and terminates transmission ofthe corresponding packet [S75]. In case that the user equipment hasreceived NACK from the network and new radio resources has not beenallocated to the user equipment, the user equipment considers that thenetwork has failed to successfully receive the packet and transmits aretransmission packet [S76].

According to the present invention, transmission reliability of ACK orNACK and communication efficiency in a mobile communication system canbe increased.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to such a wireless communicationsystem as wireless Internet, mobile communication system and the like.

What is claimed is:
 1. A method of transmitting packets at a userequipment in a mobile communication system, comprising: transmitting afirst packet to a network; and transmitting a second packet to thenetwork regardless of a reception status signal for the first packet,when control information for the second packet is received from thenetwork.
 2. The method of claim 1, wherein the control informationcomprises an uplink scheduling grant message allocating uplink resourcesfor transmitting the second packet.
 3. The method of claim 1, whereinthe second packet is not a retransmission packet.
 4. The method of claim1, further comprising: receiving the reception status signal for thefirst packet from the network; and obtaining a negative acknowledgementsignal (NACK) by decoding the reception status signal.
 5. The method ofclaim 1, wherein the mobile communication system is based on anorthogonal frequency-division multiplexing (OFDM) scheme or anorthogonal frequency-division multiple access (OFDMA) scheme.
 6. A userequipment for transmitting packets in a mobile communication system, theuser equipment being adapted to perform the steps of: transmitting firstpacket to a network; and transmitting a second packet to the networkregardless of a reception status signal for the first packet, when anuplink scheduling grant message allocating uplink resources for thesecond packet is received from the network.
 7. The user equipment ofclaim 6, wherein the control information comprises an uplink schedulinggrant message allocating uplink resources for transmitting the secondpacket.
 8. The user equipment of claim 6, wherein the second packet isnot a retransmission packet.
 9. The user equipment of claim 6, whereinthe user equipment being further adapted to perform the steps of:receiving the reception status signal for the first packet from thenetwork; and obtaining a negative acknowledgement signal (NACK) bydecoding the reception status signal.
 10. The user equipment of claim 6,wherein the mobile communication system is based on an orthogonalfrequency-division multiplexing (OFDM) scheme or an orthogonalfrequency-division multiple access (OFDMA) scheme.